Tuesday, April 25, 2006

Diesel Engines-Cat 3116 injector seating tool


Cat 3116 diesel engines require the proper tools when making any adjustments. One tool that is required is the injector seating tool. This diesel engine has unit style injectors that are seated into cups in the cylinder head.
If you don't properly seat the injectors when replacing or re-installing there is a possibility of compression blow-by which will pressurize the fuel system. I talked about this in a previous post, the fuel tank will build up pressure and your diesel engine will run verrry rough!
I experienced this first hand because I did not seat the injectors at all and relied on the injector hold-down clamps. This caused a lot of extra work, so our shop invested in the hold-down kit 'Cat # 173-1530'

Also when installing the injectors I use the sealing o-ring that fits over the injector tip [not specified for new injectors] this adds to the injector sealing capabilities.

The Cat 3116 seating tool is easy to use [it comes with an instruction manual] Just fit it over the installed injector [injector hold-down clamp torqued] then torque seating tool to 25 ft. lbs wait then retorque. Retorque injector hold-down clamp to 9 ft. lbs. [+ or - 2 ft. lbs.]

I highly recommend the seating tool for any of you doing your own repairs on a 3116 Diesel Engine.


Anonymous said...

They changed the area of the seat angle on the injector, and in the literature sent with the new injectors tell you not to put the lower tip seal on the injector. The change in the injector seat area made a better seat in the sleeve, when the seating tool is used. The seal will deteruate from heat and tens to let the injector loosen. Have put many of injectors in and have had no problems with leakage, when not puting the seal in. I also always ream the sleeve, after rebuilding cyl. head with new sleeves.

Anonymous said...


I have a friend with twin 3116 engines in his boat. We were out this weekend and when we got over about 1500 RPM one engine started to drop RPm a little and it definitely was going rich due to the extra smoke noticed. There wasn't any injector rapping or noise just a smooth RPM drop 50 to 200 RPM. Is this a symptom of injector seating problems. I was thinking of installing a piece of clear fuel line in the return and looking for air bubbles.


John Whelan said...

Reply to 1st comment: Concerning injector seating I don't use the o-rings anymore on the injector tips since there is a memo that comes with every rebuilt injector not to use them. Good advice.. thanks for the info!

Comment #2 from Joe. I would start with air in the fuel first and fuel filters etc. the white smoke is usually unburned fuel. Check the steel fuel lines running along the block on the governor side for any rubbed through areas. I've replaced several of these lines in the past that caused an air in fuel condition.

Ed said...

We got a 96 3116 in with a bad injector. We replaced the injector and associated rocker arm pieces but did not press the injector into place.

When we restarted the engine it made white smoke.

I took off the elbow after the fuel pressure regulator valve and hooked up a length of clear 3/8 in hose. We saw a steady stream of fine bubbles and an occasional 3/16" buble every three seconds or so.

My question is what is normal. I pulled the elbow from an engine that was not smoking and noted that there were a lot fewer small bubbles and a lot less frequent larger bubles.

I'm ready to call CAT and order the injector seating tool, but would like a second opinion.

John said...

Usually idf the injector isn't seated properly you will get a pressure build up in the return side and pressurize the fuel tank. There will be traces of air but it shouldn't be constantly building as the engine warms up.

Ed said...

The instructions with the Cat injector seating tool say to replace the sleeves or inspect and ream the existing sleeves. Is the ream a special Cat tool?

John said...

hi Ed,
Yes this a another Cat Tool. We had them come to our shop and do the reaming job there.
However, if the seats look OK then you can go ahead and use the seating tool. It depends on the mileage and if there are any unusual wear marks. The rebuilt injectors available now don't require the o-ring on the tip and they are designed to seat themselves. It's your call, I realize the work involved. Any doubt I would get the reaming done or replace the seats.

vince said...

i am have trouble with two injectors when i tighten allen screw to hold them down the inj binds as i move rack . i used inj seatig tool . can you help john. thanks vince

J. E. Whelan said...

Is this happening with the rockers on? The only time I had a binding problem was when the injector return spring was not compressed enough.

You probably already know that the injectors have to be slightly compressed for the injector rack to move freely.

When you tighten them down this may be deflecting the position of those 2 injectors. (They don't use orings on the tips anymore) If you're using the seating tool that should position the injector bang on in the head.

I would check the rack movement and double check the injector position.

Jeff Casey said...

First thank you for all the solid advice regarding the cat 3116, i was hoping to find someone who is willing to loan, rent, lease or last resort sell a injector cup seating tool if you know anyone what may be interested please have them email or phone me asap before this truck ends up in the atlantic ocean...........

eagles tree mx said...

hello, i have a problem also with 1997 gmc 8500 with the 3116 i have replaced the fuel filter and drained the tank ,put in new fuel .the truck idles like crap and most the time stalls however when i rev it chug a lug up then starts running beautifully until i let off the pedal and it drops to a idle then i have to chug a lug back up to a good rev im lost any ideas

John Whelan said...

eagles tree mx
check the fuel supply lines for cracks or pinholes. This happened to our engines several times. It sounds like you have air in the system. White smoke out the exhaust is an indicator. Another problem could be compression getting into the fuel through the injector seats pressurizing the fuel tank. Pressure from the tank when removing the fuel cap is the indicator.

urgentcareguy3 said...

Any special tools required to remove a 3116 turbo? The exhaust manifold flange nuts seem to be hard to get at. Thanks!

John Whelan said...

Much easier to remove complete exhaust manifold. The gaskets should be replaced if you're working on the turbo.